Chemical etching, sometimes referred to as chemical milling, is a process by which corrosive chemicals are used to engrave patterns into a substrate. Chemical etching is achieved by applying to the substrate a masking material or coating which resists the corrosive properties of the chemical etchant. The coating is then removed from the areas that are to be etched to form a desired pattern, which is then exposed to the chemical etchant.
Chemical etching is commonly used to carve into the exteriors of ferrous alloy or other metal objects which are not easily engraved by other means. Interior scribing and etching, however, has heretofore not been possible due to the lack of appropriate tools and processes. No technology for scribing and etching the internal surfaces of hollow, three-dimensional objects or shapes composed of ferrous alloy or other substrate is readily available.